Aerial vehicle speed error correlation method for two-dimensional visual reproduction of laser radar imaging

ABSTRACT

An aerial vehicle speed correlation method for two-dimensional visual reproduction of laser radar images of the present invention is capable of altering and controlling the output timing of the invention&#39;s laser radar system rated output lines based on the moving distance and the speed of an aerial vehicle. The speed error correlation method of the present invention is not limited to outputting one output line for every scanned line (N) for reducing the accumulation of geometric distortion error along the in-track direction of the scan frame. The speed correlation method of the present invention uses a set of generated fire table of equation to correct tangential error along the cross-track direction and to improve the reproduction quality of the laser radar images.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an error correlation method forimproving the quality of images photographed by an aerial vehicle usinglaser radar. More specifically, the present invention relates to the useof disclosed algorithms, which do not increase the system complexity andyet reduce the accumulation of in-track geometric distortion errorduring photographing. The present invention also discloses a fire tableof equations used to improve the reproduction quality of the laserimages by reducing tangential error accumulation in the cross-trackdirection during photographing.

2. Related Prior Art

The use of aerial vehicles to obtain aerial photographs of, for example,an object, a terrain or a plant, etc. on the ground is well known toindividuals skilled in the art. Aerial laser photography is an essentialpart of commercial, military and economic information gatheringactivities. Aerial laser photography uses the fundamentals of “points”,“lines” and “planes” to obtain desired photographs. Aerial laserphotographs are produced by performing in-track point by point scanningwith instant, one-shot laser pulse using rotational scan lenses, whilean aerial vehicle maintains relative speed and travels in an orthogonaldirection to establish a two-dimensional photograph. Each pixel of anobtained laser photograph is sampled at a different time. Theoperational mechanism of laser photography is quite different from theoperational mechanism of conventional, camera-based photography whichoperates as a one time exposure and collects pixels one by one to formthe desired photographs.

Because geometric distortion occurs in aerial laser radar photographsdue to differences in both the sampling timing and the length of thesampling timing related prior arts have suggested two approaches forreducing in-track geometric distortion of aerial laser radar photographsby uniformly distributing the pixels across the photographs. The firstapproach is based on controlling the rotational speed of the scanninglens of the laser photographic system while keeping the relative speedof the aerial vehicle constant. The second approach is based onmaintaining the rotational speed of the scanning lens of the laserphotographic system at the existing speed of the aerial vehicle.

In the first approach, the related prior art uses fixed rotational speedduring scanning while keeping the aerial vehicle at a constant speed soas to obtain laser radar photographs based on optimum in-track scanresolution. This approach is not without fault. When the laser radarphotographic system is photographing from an aerial vehicle at highacceleration and high altitude it is difficult to maintain constantspeed for a long duration due to unavoidable turbulence and winddirection changes. Also, obtaining good quality photographs depend onthe performance of the laser radar itself, the stability of the relativepositioning of the laser radar and the area to be photographed. If therelative positioning of both the former (laser radar) and/or the latter(area) are not stable, the photographs obtained through the laser radarsystem will be geometrically distorted due to inconsistent scanningpoints and inconsistent lines reproduced. Aerial photographs withgeometric distortions are distorted representation of the areasphotographed and thus lack value.

In the second approach, the related prior art controls the driving motorof the rotational speed of the scanning lens of the laser photographicsystem at the existing speed of the aerial vehicle. This approachattempts to maintain the driving motor speed of the scanning lens andthe aerial vehicle speed at the same speed levels when photographing.This approach is also flawed because the response time for the motor toadjust and stabilize its speed may take as long as several seconds,especially for motors not equipped with speed reduction mechanism. Forexample, motors that use only inertia to reduce its speed may take alonger time.

In contrast to the approaches of the related prior art, the presentinvention discloses novel algorithms, which do not increase the systemcomplexity and yet reduce the accumulation of in-track geometricdistortion error during photographing. The present invention alsodiscloses a fire table of equations for improving the reproductionquality of laser images by reducing tangential error accumulation in thecross-track direction during photographing.

SUMMARY OF THE INVENTION

An object of this invention is to disclose an aerial vehicle laser radarphotographic system using a speed error correlation method formaintaining a distance between two image points at a 1:1 ratio in thein-track direction and the cross-track directions respectively; and forreproducing quality, two-dimensional, visual laser radar images.

Another object of this invention is to disclose ways of improving thequality of photographs obtained from aerial vehicles using the laserradar system of the present invention; that is by using disclosedalgorithms which lack system complexity and are capable of reducingin-track and cross track geometric and tangential distortion errorsassociated with the laser radar's vision and thereby improving thequality of photographs obtained and reproduced.

Still, another object of this invention is to disclose controlling thetiming of the rated output lines of the laser radar system of thepresent invention based on the distance and the speed of an aerialvehicle, and which are not limited to outputting one line outputted linefor every N scanned line.

Still further, another object of the present invention is to disclosereplacing the preset system rated output line data with a proximatescanned line data when N>1 and when N=1 to compensate and to correct thelaser radar system preset rated output lines.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of this invention will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 a illustrates a one dimensional photographic scanned line and atwo-dimensional photographic scanned frame of the laser radar system ofthe present invention;

FIG. 1 b illustrates a tangential distortion correction diagram alongthe photographic cross-track direction of the laser radar system of thepresent invention and accompanying variables used to generate fire tableequations to control the laser radar emission timings of the presentinvention;

FIG. 2 illustrates a system hardware block diagram of the presentinvention. The diagram illustrates an I/O interface for storing data, adigital signal processor (DSP) for performing calculation and a fieldprogrammable gate array (FPGA) for system control;

FIG. 3 is a process block diagram illustrating a macroscopic overview ofthe radar system photographic operation of the present invention;

FIG. 4 a is a block diagram illustrating the aerial vehicle speed errorcorrelation process substeps of the radar photographic system of thepresent invention for two-dimensional visual reproduction when N>1;

FIG. 4 b is a block diagram illustrating the aerial vehicle speed errorcorrelation process substeps of the radar photographic system of thepresent invention for two-dimensional visual reproduction when N=1;

FIG. 5 illustrates the best timing for replacing the radar photographicsystem's rated output lines with proximate scanned lines to serve asoutputted vision lines when N=3, wherein the heavy lines indicate thepositions of the outputted vision lines data;

FIG. 6 illustrates the best timing for replacing the radar photographicsystem's rated output lines with proximate scanned lines to serve asoutputted vision lines when N=1, wherein the heavy lines indicate thepositions of the outputted vision lines data and the dotted lines in theslow fly column indicate those lines being abandoned;

FIG. 7 illustrates the laser radar system of the present invention beingused in a mountainous area to obtain one-dimensional photographicexperimental data; and

FIG. 8 illustrates the laser radar system of the present invention beingused on a golf course to obtain experimental speed correlation datathereof.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of modeling simplicity and clarification, the descriptionof the preferred embodiment provided below is based on threeassumptions. First, the ground surface beneath an aerial vehicle usedwhile performing laser radar photography using the present invention isa plane surface. Second, an aerial vehicle used while performing laserradar photography using the present invention maintains a constantaltitude with respect to the ground surface below. Third, an aerialvehicle used while performing laser radar photography using the presentinvention encounters no lateral wind.

As shown in FIG. 1 a, the laser radar photographic system of the presentinvention mounted on an aerial vehicle such as an airplane is used toscan along a cross-track direction to generate one-dimensional,photographic scanned lines and along an in-track direction to generatetwo-dimensional, photographic scanned two-dimensional, photographicscanned frames and their corresponding two-dimensional photographs. Whenthe radar system is initially turned on scanning occurs along thecross-track direction and as the aerial vehicle travels along thein-track direction a two-dimensional scanned frame is generated fromwhich desired two-dimensional laser radar photographs are subsequentlyobtained.

To obtain desirable laser radar photographs both geometric distortionaccumulation along the in-track direction and tangential distortionaccumulation along the cross-track direction must be minimize or totallyeliminated. During the scanning process along the cross-track directionthe laser radar of the present invention rotates its three-facet mirroralong a 120 degrees angle. The number of light point energy emitted bythe laser radar corresponds to the number of points within a scannedline. Thus if one light point energy is emitted then one point willexist within a scanned line and if N light points energy are emittedthen N points will exist within a scanned line. During scanning areference point is marked on the motor controller of the radar system asan index point and the timings (or relative emission angle) of allemitted light points are referenced with respect to the index point, andthe light points are emitted at a certain relative angle to the indexpoint. Consistent with the laser's light transmission speed and underideal conditions the timings of the emitted laser light points and thereflected image points should appear simultaneously. What actuallyhappens is that the emitted laser light points and the reflected imagepoints do not appear simultaneously, but rather when the light pointsare emitted at equal angles the distance between the image pointsappeared unequally.

FIG. 1 b illustrates the method of reducing tangential distortionaccumulation along the cross-track direction of the laser radarphotographic system of the present invention, which resolves theaforementioned problem of unequal image point distance. Theaforementioned problem is resolved through the laser radar's ability togenerate and use a fire table of equations to improve the reproductionquality of the laser images and to reduce tangential error accumulationin the cross-track direction during photographing by maintaining equalimage point distances.

Specifically, FIG. 1 b illustrates a process of generating tangentialfire table equations for an image point at a first distance (n) and foran image point at a second distance (n−1) along the cross-trackdirection. For simplicity, we have chosen to describe the left sidealong the cross-track direction in FIG. 1 b. This is because the rightside along the cross-track direction can be mapped from the left sidebecause of their symmetrical relationship. The parameters used togenerate a set of tangential fire table equations based on the left sideof FIG. 1 b are defined as follows:

m—describes the distance between X_(n) and X_(n−1), i.e. m=X_(n)−X_(n−1)

X_(n)—describes the distance between the image point (pixel_(n)) and thepoint right beneath the aerial vehicle.

X_(n−1)—describes the distance between the image point (pixel_(n−1)) andthe point right beneath the aerial vehicle.

H_(n)—describes the distance from the aerial vehicle to the earthbeneath.

S—describes the distances from the laser radar system mounted on theaerial vehicle to the image points (n and n−1).

θ—describes the angle between two distances: the distance from theaerial vehicle to image point one (n) and the distance from the aerialvehicle to image point two (n−1).

σ—describes the angle between the perpendicular distance from the aerialvehicle to the earth beneath and from the aerial vehicle to the firstimage point (n).

Based on the illustration of FIG. 1 b and the aforementioned parametersdefined above, the following fire table equations and related tangentialrelationships are generated:tanσ=X _(n) /H;  (1)tan (σ−θ)=X _(n−1) /H;  (2)σ=arc tan (X _(n) /H), the emission angle of image point one (n)  (3);andσ−θ=arc tan (X _(n−1) /H), the emission angle of image point two(n−1).  (4)

And a set of general tangential fire table equations based on FIG. 1 bare expressed as follows:pixel n: σ_(n)=σ=arc tan( m*n/H) at distance X _(n)  (5)pixel n−1: σ_(n−1)=arc tan(m*(n−1)/H) at distance X _(n−1)  (6)pixel n−2: σ_(n−2)=arc tan(m*(n−2)/H) at distance X _(n−2)  (7) pixel n−i: σ _(n−i)=arc tan(m*(n−i)/H) at distance X _(n−1)  (8)

The aforementioned generation method and parameters of FIG. 1 bdescribed above are used to generate a set of fire table equations foruse by the laser radar photographic system of this present invention.The fire table equations corrects the corresponding geometric positionof the earth and maintain the distance consistency between theindividual image points. This approach illustrated in FIG. 1 b is usedto generate relevant fire table equations for an aerial vehicle atvarying altitudes while maintaining the resolution consistency along thecross-track direction of the laser radar photographic system of thepresent invention.

The ratio of the cross-track scanned point distance (m=X_(n) (pixeln)−X_(n−1) (pixel−1)) used in the generation of the fire table equations(Equations 5, 6, 7 and 8) to the ratio of the distance between scannedlines/outputted vision lines (LD) discussed subsequently is maintainedat 1:1. An LD/m ratio of 1:1 is critical for maintaining accuratedistance between two image points alone both the in-track andcross-track directions. The responsibility of maintaining a 1:1 ratiofalls on the laser system's output transmission timing, which iscontrolled by process control steps 1 through 7 depicted in FIG. 3 ofthe present invention. In short, when LD=m the geometric and thetangential distortions along the in-track and the cross-track directionsrespectively are minimized and the reproductive quality of the laserradar images are greatly enhanced.

FIG. 2 illustrates a system layout of the laser radar photographichardware system of the present invention. The system's interface I/Ocollects data such as the light points, spacing data, resolution data,flight altitude data and flight speed data. The data collected throughthe system's I/O is stored in the Dual Port Ram Memory. The digitalsignal processor (DSP) uses the data stored in the memory to calculatethe rotational speed of the motor and to generate and calculate the firetable equations. Finally, through activation of the Field ProgrammableGate Array (FPGA), the DSP controls the motor rotational speed, thetransmitter module and the receiver module of the laser radarphotographic system hardware of the invention.

FIG. 3 is a flow chart process illustrating an operational overview ofthe laser radar system of the present invention. Referring to FIG. 3, astep 1 of starting the laser radar system and a step 2 of inputting therequired system parameters (flight altitude data and light pointsspacing data, etc) are initials steps of the process of obtainingvaluable two-dimensional laser radar photographs of the presentinvention. A step 3 of determining the laser radar hardware rotationalmotor speed to maintain the image light points spacing along thecross-track and in-track direction and a step 4 of creating a set offire table equations for correcting tangential distortions along thecross-track direction of the scanned frame are further initial processsteps of obtaining two-dimensional laser radar photographs. In a step 5and a step 6 respectively, the system triggers the laser radar inaccordance with the fire table equations tangential correction andcollects the reflected signals. Step 7 deals with the laser imageresolution correction and is the most critical process step of thepresent invention. Correlation resolution correction is performed eachtime a scanned line from a facet mirror is completed. After resolutioncorrection in step 7 the resulting image is displayed in a step 8 andthe process ends in a step 9.

Pursuant to the previous paragraph, FIG. 2 step 7 is the most criticalprocess step of the present invention. At step 7, image resolutioncorrection occurs and accumulated in-track geometric distortion error isgreatly reduced. The present invention teaches two unique algorithmsused at this process step, which do not increase the system complexityand yet reduce the accumulation of the in-track geometric distortionerror during photographing. The first algorithm is for correcting imageresolution by reducing in-track geometric distortion when N>1—whenmultiple scanned vision data is outputted for a single scanned line (N).The second algorithm is for correcting image resolution by reducingin-track geometric distortion when N=1—when a single scanned vision datais outputted for a single scanned line (N).

FIG. 4 a, which is a first preferred embodiment of this invention,illustrates the first algorithm flow chart diagraming substeps of step 7in FIG. 3, for correcting image resolution by reducing in-trackgeometric distortion when N>1. FIG. 4 b, which is a second preferredembodiment of this invention, illustrates the second algorithm flowchart diagraming substeps of step 7 in FIG. 3, for correcting imageresolution by reducing in-track geometric distortion when N=1. Theparameters used in both the first algorithm and the second algorithm aredefined as follows:

N—describes a quantity of scanned vision data outputted for scannedvision line s.

V_(o)—describes an initial preset speed of an aerial vehicle immediatelyprior to photographing.

V_(r)—describes an actual aerial speed at the time of photographing.

DIST—describes a line distance between each scanned line.

RESL—describes a system rated output line distance (RESL=N×DIST).

Dahead—describes a balance of a moving distance of an aerial vehiclesince the last outputted data; wherein the balance can be a positive ora negative number and the initial value is set at zero.

Rd—describes a ratio of the Dahead to the system output line distance.

IPF—describes an interpolation flag of the algorithm.

LD—describes a distance between outputted vision lines.

Now referring to FIG. 4 a, for N>1, after receiving the laser radarsignal/data at step 7 and after completing at least one scanned line atsubstep 7 a ₁, proceed to substep 7 a ₂ for calculating an LD value, forcalculating a Dahead value and for calculating an Rd value by performingDIST*Vr/Vo, Dahead+LD and Dahead/RESL respectively. If however substep 7a ₁ does not result in at least one complete scanned line then result toperforming step 7 again by receiving the laser radar signal/data untilat least one scanned line is complete. If, however, the calculated Rdvalue in substep 7 a ₂ is greater than 2 then perform substep 7 a ₃ bysetting the Dahead value equal to zero followed by outputting thecurrent vision line data pursuant to substep 7 a ₄ and subsequentlyreturning to receiving laser radar data in step 7.

Still referring to FIG. 4 a of the present invention, if the calculatedRd value in substep 7 a ₂ is less than 2 but greater than 1 or if thecalculated Dahead value plus the calculated LD value is greater than theRESL value in substep 7 a ₅ then result to performing substep 7 a ₆ bycalculating the current Dahead value by subtracting RESL from theexisting Dahead value followed by outputting the current vision linedata pursuant to substep 7 a ₇ and subsequently returning to receivinglaser radar data in step 7. If, however, the calculated Dahead valueplus the calculated LD value divided by two is not greater than the RESLvalue then return to receiving laser radar data in step 7.

Now referring to FIG. 4 b, for N=1, after receiving the laser radarsignal/data at step 7 and after completing at least one scanned line atsubstep 7 b ₁, proceed to substep 7 b ₂ for calculating an LD value, aDahead value and an Rd value by performing DIST*Vr/Vo, Dahead+LD andDahead/RESL respectively. If however substep 7 b ₁ does not result in atleast one complete scanned line then result to performing step 7 againby receiving the laser radar signal/data until at least one scanned lineis complete. If the calculated Rd value in substep 7 b ₂ is less than0.5 then return to step 7 by receiving incoming laser radar signal/data.If, however, the calculated Rd value is greater than or equal to 0.5then proceed to substep 7 b ₃ by calculating the current Dahead value bysubtracting the existing RESL value from the existing Dahead value,followed by performing substep 7 b ₄ by outputting the current visiondata line and subsequently returning to step 7 by receiving incominglaser radar signal data.

Still referring to FIG. 4 b of the present invention, if the calculatedRd value is greater than 1.5 and if the IPF is turned off then performsubstep 7 b ₅ by calculating the current Dahead value by subtracting theexisting RESL value from the existing Dahead value, followed by turningthe IPF on in substep 7 b ₆, saving and outputting the current visionline in substep 7 b ₇ and subsequently returning to step 7 by receivingincoming laser radar signal and data. If, however, the IPF is turned onthen performed substep 7 b ₈ by interpolating the previous and currentvision line data, followed by outputting the interpolated vision linedata and outputting the current line data in substeps 7 b ₉ and 7 b ₁₀respectively. Finally perform substep 7 b ₁₁ for turning the IPF offfollowed by substep 7 b ₁₂ for calculating the current Dahead value bymultiplying NDL2L by two and subtracting the obtained value from theexisting Dahead value and subsequently performing step 7 for receivingincoming laser radar signal/data.

The algorithms disclosed in FIG. 4 a and FIG. 4 b also reduce andmaintain accumulated geometric distortions based on the moving distanceand the speed of the aerial vehicle by controlling the timing forreplacing the laser radar system's preset, rated output lines withproximate scanned lines which are outputted as vision lines. Beforeusing the laser radar to photograph pictures, for example when N=1, theaerial vehicle's speed is set to its initial value V_(o) in accordancewith the laser radar's motor rotational speed for driving the radar'sthree facets mirror to ensure that every scanned line (N) outputs onevision line data, and to maintain the scanned lines spacing at aconstant. Inevitably, air turbulence changes the aerial vehicle's speedfrom V_(o) to V_(r) thereby varying the line spacing between the scannedlines and thus accumulating geometric distortions. Thus controlling thetiming for replacing the system's preset output lines is critical forcontrolling the distance between two successive scanned lines, which inturn is critical for controlling the quantity of geometric distortionsexhibited in the laser radar photographic images.

FIG. 5 illustrates the three distinct columns of scanned lines and theircorresponding outputted vision lines for N>1, corresponding to the firstpreferred embodiment of this invention: the right column represents theaerial vehicle photographing at high speed; the left column representsthe aerial vehicle photographing at a constant speed; and the middlecolumn represents the aerial vehicle photographing at a slow speed. Thefaster the aerial vehicle travels while photographing the wider thedistance from one scanned/vision line to another. In contrast, theslower the aerial vehicle travels while photographing the shorter thedistance from one scanned/vision line to another. Thus, if the rightcolumn is compared to the left column the line spacing in the rightcolumn is wider than the left column for the identical flying duration.Similarly, if the left column is compared to the middle column the linespacing of the left column is wider than the middle column for theidentical flying duration.

Still referring to FIG. 5, the left “constant speed” column, where N=3,outputs one vision line for every three scanned lines. The middle “slowspeed” column does not output one vision line for every three scannedlines, instead one vision line is outputted for every three or fourscanned lines, which increases geometric distortions due to theinconsistent number of outputted scanned lines. For the middle “slowspeed” column the outputted data lines are numbered 0, 4, 8,11, 15 . . ., and the system's preset, rated output lines data are replaced withproximate scanned lines data, which are then converted to scanned visionlines data. A similar phenomenon is observed in the right “fast speed”column, where one outputted vision line is not outputted for threescanned lines. Instead one vision line is outputted for every two orthree scan lines, which also increases geometric distortions due to theinconsistent number of outputted scanned lines. Therefore, the besttiming for controlling and replacing the laser radar system's preset,rated output lines with proximate scanned lines which are outputted asvision lines is illustrated in the left “constant speed” column for N=3.Unlike the right “fast speed” column and the middle “slow speed” column,the left “constant speed” column constantly outputs one vision line forevery three scanned lines and thus effectively controls and maintains aneven distance between the scanned lines, which is critical in preventinggeometric distortion accumulation.

FIG. 6 illustrates another three distinct columns of scanned lines andtheir corresponding outputted vision lines for N=1, corresponding to thesecond preferred embodiment of this invention: the right columnrepresents the aerial vehicle photographing at high speed; the leftcolumn represents the aerial vehicle photographing at a “slow speed”;and the middle column represents the aerial vehicle photographing at a“constant speed”. For the middle “constant speed” column one vision lineis outputted for one scanned line. In contrast, for the left “slowspeed” column not every scanned line outputs a vision line. Instead someof the lines are illustrated as dotted and abandoned. Still referring toFIG. 6, the outputted data lines of the left “slow speed” column arenumbered 0-1, 3-5, 7-9, 11-13 . . . , the dotted abandoned lines are 2,6, 10 . . . , and the system's preset, rated output lines data arereplaced with proximate scanned lines data which are then converted toscanned vision lines data. Finally, for the right “fast speed” columnevery scanned line does not directly output one vision line. Insteadsome scanned lines must undergo average interpolation to ensure that thesystem outputted vision lines are in compliance with the system ratedoutput lines. Referring to the right “fast speed” column of FIG. 6, thelines numbered 2 and 3, 6 and 7 and 10 and 11 undergo averageinterpolation prior to replacing the system's preset, rated output lineswith proximate scanned lines which are outputted as vision lines.

Using the algorithms illustrated in FIG. 4 a and FIG. 4 b the timing forreplacing the system's preset output lines is controlled and the linespacing of the rated output lines is usually between 0.5 and 10 meters,and except for a few land terrain photographs the resolution of mostland terrain photographs are within this range. When photographs aretaken from an aerial vehicle flying above 500 meters the variation ofthe terrain or the landform is of little significance. FIG. 7 and FIG. 8further illustrate and experimentally corroborate the unique andadvanced features of the speed error correlation method of the presentinvention.

FIG. 7 illustrates a one-dimensional photograph of a mountainous areaused for obtaining experimental data. A single x axis or the abscissarepresents the system rated output lines. In contrast the y axis or theordinate is divided into a right ordinate and a left ordinate. The rightordinate represents the aerial vehicle speed (m/s) and the left ordinaterepresents the terrain height. Towards the left portion of FIG. 7, thelowest curve represents the cross sectional view of the aerial speedduring photographing with the laser radar (V-LR). The uppermost dottedline, which is indicative of geometric distortion, represents thecentered surface cross sectional view of the distance vision line(ORI-L) prior to applying the speed error correlation of the presentinvention, and the solid line represents the centered surface crosssectional view of the distance vision line (SC-L) after applying thespeed error correlation of the present invention. Both curves arecompared to a middle reference curve (DTM) which represents an actualcentered terrain cross sectional view.

Still referring to FIG. 7, for effective comparison to the actualterrain centered cross sectional view (DTM), the height of the centeredsurface cross sectional view of the distance vision line (ORI-L) ispositioned upwards prior to applying the speed error correlation methodof the present invention. Similarly, the height of the centered surfacecross sectional view of the distance vision line (SC-L) is positionedupwards after applying the speed error correlation method of the presentinvention. The comparison shows that as high speed laser photographingoccurs, the line spacing between the ORI-L and the SC-L on one hand andthe DTM on the other hand narrowed, and the dotted ORI-L curve(containing geometric distortions) is depressed. Such results furthervalidate that the aerial vehicle speed error correlation method forreproducing two-dimensional laser radar is capable of timely correctingaccumulated geometric errors due to high and unstable aerial speed.

FIG. 8 shows photographic results from the laser radar of the presentinvention when used to obtain experimental, speed-correlated visionlines data of a golf course. The photographs on the right, left andmiddle of FIG. 8 are a reference golf course image, an actual golfcourse image using the error-correlated method of the present inventionand a superimposed error-correlated golf course image on the referencegolf course image respectively. The white rectangular frame shown on thecenter of the middle photograph indicates that the speed errorcorrelation method of the present invention indeed improves the qualityof the laser radar photographs of the present invention.

Finally, the aerial vehicle speed error correlation algorithms describedin FIG. 4 a and FIG. 4 b are executed with no complexity, are simple andpractical and are in compliance with the real requirements of thesystem's functions. Furthermore, the method of this invention results inhigh quality photographs and thus further reduces the costs associatedwith reproducing these photographs.

While particular embodiments of this invention have been shown in thedrawings and description above, it will be apparent that many changesmay be made in the form, arrangement and positioning of the variouselements of the combination. In consideration thereof it should beunderstood that the preferred embodiments of this invention disclosedherein are intended to be illustrative only and not intended to limitthe scope of the invention. Any modifications are within the spirit andscope of the invention, which are limited and defined only by theappended claims.

1. An aerial vehicle laser radar photographic method using tangentialand geometric speed error correlation algorithms for two-dimensionalvisual reproduction of laser images when N>1 comprising the steps of:receiving photographic laser radar signal data; scanning at least onecomplete line; calculating an LD value as DIST*Vr/Vo, where DISTdescribes a line distance between each completed scanned line, Vrdescribes an actual aerial speed at the time of photographing and Vodescribes an initial preset speed of an aerial vehicle immediately priorto photographing; calculating a Dahead value as Dahead+LD, where Daheaddescribes a balance of a moving distance of an aerial vehicle since thelast outputted data, wherein the balance can be a positive or a negativenumber with an initial value set at zero, and LD describes a distancebetween outputted vision lines; and calculating an Rd value asDahead/RESL, where RESL describes a system rated output line distanceand Rd describes a ratio of the Dahead to the system output linedistance; and outputting scanned line(s) as vision line data andreplacing the laser radar's preset rated output line data with proximatescan line data after resetting a Dahead value to zero and if said Rdvalue calculated is greater than 2 and a moving distance of an aerialvehicle has exceeded two lines distance of the laser radar system'spreset rated output lines; and thereby reproducing two-dimensionalvisual laser radar images for N>1 by restricting geometric distortionerrors to within one system rated output line distance, where Ndescribes a quantity of scanned vison data outputted for scanned visionlines.
 2. An aerial vehicle laser radar photographic method usingtangential and geometric speed error correlation algorithms fortwo-dimensional visual reproduction of laser images as forth in claim 1further comprising the steps of: calculating a Dahead value asDahead−RESL, when Rd is greater than 1 or when Dahead+LD/2 is greaterthan RESL; outputting completed scanned line(s) as vision line data; andreplacing the laser radar's preset rated output line data with proximatescan line data.
 3. An aerial vehicle laser radar photographic methodusing tangential and geometric speed error correlation algorithms fortwo-dimensional visual reproduction of laser images when N=1 comprisingthe steps of: receiving photographic laser radar signal data; scanningat least one complete line; calculating an LD value as DIST*Vr/Vo, whereDIST describes a line distance between each completed scanned line, Vrdescribes an actual aerial speed at the time of photographing and Vodescribes an initial preset speed of an aerial vehicle immediately priorto photographing; calculating a Dahead value as Dahead+LD, where Daheaddescribes a balance of a moving distance of an aerial vehicle since thelast outputted data, wherein the balance can be a positive or a negativenumber with an initial value set at zero, and LD describes a distancebetween outputted vision lines; and calculating an Rd value asDahead/RESL, where RESL describes a system rated output line distanceand Rd describes the ratio of the Dahead to the system output linedistance; and abandoning said complete scanned line(s) when Rd is lessthan 0.5; outputting said complete scanned line(s) as vision line datawhen Rd is greater or equal to 0.5 subsequent to calculating a Daheadvalue as Dahead−RESL; and thereby reproducing two-dimensional visuallaser radar images for N=1 by restricting geometric distortion errors towithin one system rated output line distance, where N describes aquantity of scanned vison data outputted for scanned vision lines.
 4. Anaerial vehicle laser radar photographic method using tangential andgeometric speed error correlation algorithms for two-dimensional visualreproduction of laser images as forth in claim 3 further comprising thesteps of: calculating a Dahead value as Dahead−RESL, setting the IPF,the algorithm interpolation flag, on if the IPF is turned off, andsaving and outputting current vision line data when said Rd value isgreater than 1.5; interpolating previous and current vision line data ifthe IPF is turned on; outputting interpolated vision line data;outputting current line data; setting the IPF off; and calculating aDahead value as Dahead−RESL*2.
 5. An aerial vehicle laser radarphotographic method using tangential and geometric speed errorcorrelation algorithms for two-dimensional visual reproduction of laserimages as forth in claim 4 further comprising the steps of: compensatingsaid error correlation method using interpolation; and correcting saiderror correlation method using interpolation.